Electrodes for voltolization



March 3, 1942. R. w. RICHARDSON ET AL 2,274,636

ELECTRODES FOR VOLTOLIZATION Filed Sept. 21, 1958 Patented Mar. 3, 1942 PATENT QFFICE ELECTRODES FOB VOLTOLIZATION Roger W. illrf 'is,

n, Wcstileld, and George L.

Mathesom, Union, N. 1., assignors to Standard Oil Development Company, a corporation of Delaware 7 Claims.

This invention relates to improvements in apparatus for treating carbonaceous materials with silent electric discharges, and more purticularly to an improvement in. the electrodes of such apparatus.

Electrical treatments of carbonaceous materials, such us fatty and hydrocarbon oils, fats, and waxes, and other organic compounds, whereby such materials ore subjected to the action of high irequehoy electric discharges at high potentials but below those at which spurlziug occurs have been commonly designated as voltolizatiou processes. The action of silent electric discharges on the organic compounds is complex and varies with factors including pressure, electrical potential, current, and frequency, which are readily controlled. end other ioctors which can be broadly included in the emcieucy of construction and menlpulotiou oi the dischorge op- Paratus.

Regardless of how occurstely the factors oi pressure and electric current are controlled, or

Ject is to prepare such improved electrodes with a coating which is easily applied and which remains as an intact even layer on the electrode over a long period of service. Further objects are to provide a form and assembly of conducting electrodes which eliminates irre arities of electrical discharge intensity which may arise from the shape of the electrodes and the manner of assembling the electrodes. These and other objects will become apparent from the following description arid claims.

Although it has already been proposed to encose metal electrode sheets with layers of dielectrio material, such as porcelain, earthenware, vulcanized fiber, artificial molded resins, gloss, wood, oil soaked paper, etc., various dimcultles were experienced in trying out these materials. In being relatively thick, such layers of dielectric materiel lower the amount of electrode dischorge oi how the carbonaceous meterisls heoted ere.

manipulated, practical dimculties may arise in making the action of the electric dischorse uniform and in preventing contamination oi the product by parts of the apparatus. it small excess of charge at any localized spot on on electrode forms a nucleus of intensified reaction which in a short time builds up insoluble gels and destroys the uniformity of treatment, cousins some oi. the material to be overvoltoliued and some undervoltolized. Also, it has been observed that ii bare metal electrodes are used, the resulting product tends to be contaminated with colloidal motel, which frequently is harmful. These dificulties have been successfully avoided in accordance with the present invention by applying to discharge surfaces of each conducting electrode, particularly each metallic electrode, a

uniform and continuous adherent coating a material which prevents contact of the conductins electrode with the materiel being voltolized, and which is sumciently thin to maintain a high electrical capacity in the circuit betweeneach pair of consecutive electrodes.

An object of this invention is to provide tor more efliciently constructed silent electric discharge apparatus having improved conductin electrodes prepared by applying to the electrodes a thin. homogeneous. and uniiorm protective coating which particularly resists dissolution by the reacting materials, deterioration by the silent electric discharge, oxidation, moisture, other chemical action, and heat, A more specific and preclude an emcient use of o dielectric plate spaced from and between the electrodes. The very herd materials such as the artificial resins, porcelain, earthenware, ordinary enamels, etc., are too inflexible and are easily craclred. Also, such materials do not adhere well to the metal surface, and even when glued to the metal surface, fissures form readily between the metal and the hard dielectric layer. In general, the shellacs and enamels are unstable under the voltoliziug conditions, developing blisters and becoming broken at numerous places.

The stable and adherent protective coatin which now has been developed is a clear baking oil varnish which may be applied evenly over the electrode surface by brushing, spraying, or dipplug. The thus coated electrode may be used after sir drying without previous baking. This varnish, of the China-wood oil and linseed oil or drying oil typ is typified by the following P ysical characteristics:

Specific gravity at 20 C .900 to .910 Viscosity (Stormer) at 20 C"..- 40 to 80 seconds Non-volatile matter (minimum) 5% Drying time (A. S. T. M.) on

copper 2% hours Life test minimum (A. 5.1. M.) 1200 hours Flash Point, minimum C.

generally have a China-wood oil (tung 011) base ob linseed oil blended with combined with a relatively smaller amount of a resin such as copols,

Parts Resin 30 Gum 16 Wood oil .uinseed oil 2% With increased proportions of oil the drying time of the varnish is increased. The cookin mounted centrally on a rotatable shaft so that they rotate therewith to cause reactant liquid is carriedout at atemperature of about 300 to W 400 F. for a period of 4 to 8 hours. After thinning and filtering of the cooked varnish, a mall amount of drier of the soluble organic salt type is generally added, e. g., 0.4% of lead naphthenate. Pigments are preferably omitted.

This type of varnish after being applied to the electrode plates is allowed todry for about 24 to 48 hours before the varnished electrodes are introduced into the voltolizing apparatus. Temperatures of about 189 F. in the voltolization may bake the varnish to some extent. The varnished electrode may be air dried for a shorter period of to 16 hours followed by baking for a short period before introduction into the voltolizing apparatus if desired.

In some instances, synthetic resins or resinoids are used to replace the natural or fossil resins, and. desirable types of synthetic resins which may be thus used are polyvinyl acetal resins, alkyd resins, and some modified resins rather than phenol-formaldehyde resins. A varnish film-having a glossy finish and suiilcient elasticity for expansion with the metal through the range of operating temperatures is desired rather than a plastic varnish.

The metal surfaces to be varnished are preferably well cleaned before the varnish is applied. The metal surfaces may be polished to a smooth finish before applying the varnish, rather than roughened. With a uniform pore free varnish coating capable of adhering to a polished metallic surface, the oil undergoing treatment tends to spread out over the coating in a thin film ensuring a definite and uniform dielectric gap between the electrodes.

While apparatus in which the improved electrodes may be employed are well known in the art, the following explanations will facilitate understanding of the features in this invention.

Two main types of apparatus used for voltollzation are the tube and the trommel types. The

latter typ with which the present invention is' mainly concerned, is more suitable for large scale operation and can be more ruggedly constructed especially with the use of metallic conducting electrodes.

The trommel type of apparatus comprises a horizontal drum in which is disposed a plurality of separated conducting electrode plates having parallel discharge surfaces. Between pairs of these electrode plates may be interposed one or more non-conducting parallel plates having dielectric surfaces. The conducting electrode platesv are spaced apart by dielectric material so that sets of alternate electrode plates may be connected together with sources of alternating current to form discharges between each pair of plates. All or a number of the plates may be brought upon their surfaces to form thin films thereon. The reactant material may be brought upon the plate surfaces by means of sprays, scoops. or any means which permits the liquid to flow over the surface evenly. The rotating plates may dip into a pool of the liquid reactants at the bottom of the drum'so that they pick up liquid as they rotate. A detailed description of some specific forms the trommel type apparatus assumes is given in U. S. Patent 2,071,551, granted February 23, 1937 to George L. Matheson.

In the tube type of apparatus the conducting electrode elements and any intervening dielectric elements assume generally a vertical cylindrical form and are spaced apart by having the cylinders of different diameters and arranged concentrically. The liquid reactant is made to flow in thin films over one or more of the cylindrical surfaces by rotation of such cylinders with their lower parts immersed in a pool of the liquid, by sprays, etc. The conducting electrodes are alternately connected in sets to alternating current sources for producing alternating discharges between pairs of the cylinders.

' shaft and makes an electrical The general construction of the apparatus especially with reference to the assembly of the electrodes improved according to the present invention will be fully understood with reference to the accompanying drawing, in which:

The figure is a diagrammatic view in sectional elevation of a trommel type of apparatus. To

show the details more plainly in this view, space has been economized by omitting an intermediate portion of the trommel, in which there is only a repetition of parts shown. The omitted portion is indicated as coming between the broken lines.

Referring to the figure, which shows a crosssection in detail of an electrode assembly adapted for use in a trommel type of voltolizer, numeral i designates a rotatable bored metal shaft or axle projecting horizontally into the shell or drum 2 through a gas tight bearing 3 to socket i. Bear-,- ing 3 may be made gas tight by packing 5 held tightly packed between the threaded nut 6 and the threaded gland i. The shaft i is revolved through a driven pulley 8, or its equivalent. A series of thin conducting electrode disc-shaped plates or sheets a and id are mounted vertically on shaft 5 to be rotated therewith. The set of alternate metal discs 9 have fixed electrical contacts with the shaft 9, which may simply complots the electric circuit by being grounded through its bearing contact wi h the tromrnel drum 2, and ground wire ii. The set of alternate metal discs Iii is electrically insulated from metal shaft 5 by the dielectric plugs l2 and dielectric discs W, and is connected together with a high tension lead wire it by conducting taps Id. Lead wire i 3 is insulated from the metal shaft, by the dielectric tube within the bore of the connection with a high tension alternating current terminal it through the revolving slip ring H and brush It. The adjacent electrodes are spaced apart by dielectric discs i9 and preferably have an intervening narrow dielectric disc 20 of which the edge may extend beyond the rounded edges 2! of the electrodes. An oil scoop 22 may be supported by the two outside dielectric discs l9 for lifting liquid reactant material from the pool at aavacsc 3 neath. The drum 2 is provided with an upper outlet 23 for leading gaseous material to an evacuating means (not shown), a bottom drain and sampling pipe 20 having a valve 25, valved inlet 26 and. outlet 2] for introduction, withdrawal, and recycling of liquids, and a jacket 28 for enclosing a heat exchange medium to heat or cool drum 2 and its contents. The heat exchange fluid is introduced and withdrawn by valved inlet and outlet pipes 33 and 34.

If it is desired to use two high tension sources of alternating current in the circuit, the illustrated arrangement may be modified as shown, simply by insulating the shaft from the drum by insulating sleeves 29 and connecting the insulated shaft to a high tension terminal or bus bar 30 through a slip ring and brush combination 3 I, which canbe placed outside the, drum.

An enlarged cross-section is shown of the conducting plates 9 and ill in their preferred form for avoiding any sharp edges or points at which electricity tends to accumulate. The localized accumulation of electricity may cause metallic sputtering, localized overvoltolization, and even arcing, all of which result in a damaged product and power loss. An application of a thicker coating of varnish at the edges remedies this condition to some extent, but rounding of the edges 2| and a uniform coating of varnish 32, is preferable, the varnish being preferably of the stable types described.

The conducting electrode, leads, and taps may be constructed of any suitable conducting material, such as metals, alloys, or mixtures thereof. As suitable examples may be mentioned aluminum, copper, nickel, iron, silver, mercury, tantalum, tungsten, vanadium, platinum, molybdenum, zinc, chromium, cobalt, cadmium, etc. Metalloids such as carbon and the like may also be used.

The conducting electrodes may be in the shape of discs, disc quadrants, etc., and in the form of sheets as thin as foil and thicker or of fine mesh screen. Smooth plane discharge surfaces are, however, particularly desired.

The dielectric material used for spacing the electrodes apart, for insulating them and the leads, and in dielectric plates or sheets interposed between the electrodes may be any suitable insulating material of sufllcient strength to stand up under the high tension current and mechanical forces imposed upon them. As examples of suitable materials may be mentioned cellulosic materials and cellulose esters, fiber board, oil soaked fullerboard, vulcanized rubber, syn- Y thetic rubbers, artificial and synthetic resins,

such as coumarone resins, phenolic resins, etc., made up in single or laminated sheets. Glass, earthenware, porcelain, enamelware, etc., may be used with more precautions taken against breakage. Oil soaked fullerboard is considered one of the most practical materials for use as a dielectric between electrodes because of its durability, high dielectric properties, and low cost.

For improved efficiency it is important to have the protective coating on the electrodes as thin as possible consistent with needs for durability, to enhance the total electrical capacity and energy flow in the circuit between the electrodes. With a more highly effective electrical capacity between the electrodes, the current density, which is proportional to the rate of voltolization, is also relatively high. A desirable protective coating is obtained with a film of the varnish limited to a thickness of about 0.005 to 0.2

mm. However, a coating of this type has such high electrical capacity as to require insertion into the space between consecutive electrodes of a dielectric plate having sufficient thickness to decrease the voltage gradient at the coating and thus prevent breakdown in the coating.

For a suitably balanced circuit between the electrodes having thin protective coatings and interposed dielectric sheets, the consecutive electrodes are spaced apart by about 0.6 to 2.5 cm., and the dielectric sheet having a thickness of about 0.15 to 0.3 cm. is equidistant between two consecutive electrodes. With this arrangement and these dimensions, the protective coating will satisfactorily endure the usual silent electric tensions even though the thickness of the coating be less than 0.2 mm.

The clearance between conductors having opposite polarities should be sufiicient to prevent arcing. In a hydrogen environment having a gas pressure of about 0.1 atmosphere, arcing will not occur until the difference of potential between conductors of opposite polarity and separated by a 10 cm. gas gap is about 5,000 volts. A clearance of at least 10 cm.', therefore, will be. ample in most voltolization work. The usual voltolization process employs an alternating current of about 60 to 10,000 cycles per second, a subatmospheric pressure of about a few centimeters of mercury to about 0.5 atmosphere absolute, and a voltage of about 1,000 to 20,000 volts.

The improved varnished electrodes described, in addition to having the already noted advantages of eliminating contamination of the voltolized product by colloidal metahpermitting more uniform voltolization, preventing sparking, having a durable and inexpensive construction, are considered to be exceptionally efficient in presenting a smooth surface which is self-cleaning and which is readily wetted by the organic reactants. Exposure of continuous even films of re acting liquid to the action of silent electric discharges is one of the most essential requirements for successful voltolization, and the oil wetting property of the drying oil varnishes has been found to be highly conducive to the formation of such films.

With the-discharge surfaces of the metal or conducting electrodes entirely covered by a sufficiently thin protective, coatingwhich the varnish provides,- dielectric plates can successfully be used-between pairsof the electrodes with sumciently high voltage gradients between eachelectrode and an adjacent dielectric pl ate to substantially double the amount of reactant film surface treated per unit area of electrode discharge surface, permitting reactant films on the dielectric .plate surface to be treated as well as those on the coated electrode.

It will be understood that various modifications may be made without departing from the spirit and scope of the invention, which is not to be limited by any theories of mechanism of voltolization nor any details given merely for the purpose of illustration but only by the following claims which are intendedto define all novelty inherent in the present invention.

We claim:

1. An apparatus for subjecting thin films of carbonaceous liquid to the action of silent electric discharges comprising a source of high frequency alternating current, a plurality of separated conducting electrode plates having smooth parallel discharge surfaces, a non-conducting plate interposed between each pair of said elec- 4 terraces trode plates, means for connecting alternate electrode plates with the source of alternating current to form discharges between each pair of plates, 9, continuous, uniform, substantially flex-- ible coating film of clear air-dried and baked baking varnish over'the discharge surfaces of each of said electrode plates, said coating film having a low electric resistance, and means for bringing the carbonaceous liquid onto said varnish coatings so that the carbonaceous liquid spreads out as an even film over said coatings.

2. An apparatus for subjecting films of carbonaceous liquid to the action of silent electric discharges comprising a source of high frequency alternating current, a plurality of spaced metallic electrodes having smooth parallel surfaces, a stable, substantially flexible, protective film coating of an air-dried and baked varnish having a thickness of less than 0.2 mm. on each of said electrodes to prevent contact of the metal with carbonaceous liquid subjected to treatment, said film having a low electric resistance; a dielectric plate interposed between each pair of consecutive electrodes, with sufiicient thickness in the dielectric to prevent breakdown of the film coating, means for connecting alternate electrodes together with the source of alternating current to produce silent electric discharges between the electrodes and the interposed dielectric plate, and means for bringing the carbonaceous liquid onto the protective coating and the dielectric plate so that said liquid spreads thereon as even films which are affected by the silent electric discharges 3. An apparatus for subjecting carbonaceous materials to the action of silent electric discharges, comprising spaced dielectric members and spaced conducting electrodes adapted to 5. An apparatus according to claim3, in which said film coating has a thickness of not more than 0.2 mm.

6. In an apparatus ofthe character described, including a plurality of spaced metallic electrodes-having smooth parallel discharge surfaces with interposed spaced dielectric members, an electrode member in which all peripheral discharge surfaces are rounded to provide a substantially continuous discharge surface for said electrode, and a continuous, low resistance, substantially flexible film coating of an air-dried and baked varnish composition as a protective outer coating over the discharge surface of said electrode, said varnish insulating the electrode against surface deterioration.

7. An apparatus of the character described, comprising a plurality of evenly spaced, polished sheet metal electrodes disposed in parallel relation one to another, a plurality of dielectric elements disposed in alternate relation between said electrodes and spaced apart therefrom, and a low resistance, substantially flexible, film coating of an air-dried and baked varnish composition applied to the surfaces of said electrodes.

ROGER W. RICHARDSON. GEORGE L. MATHESON. 

